1. Field of the Invention
The present invention relates to an acoustic signal processing apparatus and method, and an audio device. More particularly, the present invention relates to the art of extracting external noise components contained in acoustic signals.
2. Description of the Related Art
In general, car audio systems have problems with noise which is present in sound playback systems. The noise makes it difficult for users to hear acoustic signals of music, etc., provided from a speaker while moving. In the related art, an audio signal supplied to the speaker is corrected based on an external noise component, such as noise present in a sound playback system.
FIG. 8 shows an acoustic signal processing apparatus of the related art for extracting external noise contained in an acoustic signal. A speaker 10 provides an acoustic signal corresponding to an audio input to a sound playback system. The sound playback system has external noise. A microphone 11 converts the noisy acoustic signal into an electrical signal, and supplies it to a subtractor 12. An FIR (Finite Impulse Response) digital filter 13 supplies a simulated impulse response of the sound playback system to the subtractor 12. The output of the FIR filter 13 corresponds to a noiseless audio signal taking the sound playback system into account, and the external noise component is provided as an output from the subtractor 12.
However, the apparatus of the related art has drawbacks. As shown in FIG. 9, the impulse response of the sound playback system in the car audio system has a length of about 4,000 sampling points given that the sampling frequency is 44.1 kHz. In other words, the FIR filter 13 must have about 4,000 taps, which makes the apparatus costly. In addition, the FIR filter 13 must perform a large number of computations, resulting in high power consumption due to heat, etc. The number of sum-of-product computations required per sampling time (1/44100 Hz≅0.023 msec) for FIR filtering by the FIR filter 13 with, for example, 4,096 taps is given by 4096×2, and the number of sum-of-product computations required per second is given by (4096×2)×44100=361,267,200.